This invention relates to artificial shoulder joints and more particularly to the glenoid component of an artificial shoulder joint.
Total shoulder arthroplasty is the replacement of the natural shoulder joint with an artificial one. Such an artificial shoulder joint will typically have a humeral component and a glenoid component. One of the humeral and glenoid components will typically have a ball and the other component will have a concave bearing surface against which the ball articulates and which comprises an articulating surface of the artificial shoulder joint. This concave bearing surface can be part of a socket which receives the ball although it can also be less than a full socket. In many cases, the humeral component will be a ball and stem where the stem is implanted in the humerus and the glenoid component will have the concave bearing surface.
When an artificial shoulder joint is implanted during total shoulder arthroplasty, the shoulder must be exposed and dislocated to some degree to provide sufficient room to permit the components of the artificial shoulder to be implanted. The amount of exposure and dislocation required is determined by the shape of the artificial shoulder joint components and the way in which they are implanted. However, the greater the degree of shoulder exposure and dislocation, the greater the trauma to the patient. It is therefore desirable to keep the amount of exposure and dislocation to a minimum.
In the past, many glenoid components for artificial shoulder joints have been implanted laterally. However, lateral implantation requires a significantly greater degree of exposure and dislocation than would be required if the glenoid component could be implanted anteriorly.
It is an object of this invention to provide a glenoid component for an artificial shoulder joint which can be implanted anteriorly to reduce the amount of exposure and dislocation required when the glenoid component is implanted.
It is another object of this invention to provide an artificial shoulder joint where the humeral component and glenoid component are adapted for use with orienting members to facilitate orientation of the humeral component with the glenoid component.
A glenoid component for an artificial shoulder joint constructed according to this invention has a retainer having an ultra high molecular weight polyethylene insert affixed thereto. The insert has a concave humerally facing articulating surface on which a ball of the humeral component articulates. The insert also has a fixation tab extending through a slot in the retainer and posteriorly from a scapular facing side of the glenoid component at an oblique angle to the articulating surface. The tab is cemented to the scapula to provide short term fixation of the glenoid component to the scapula. The retainer has a plurality of porous metal coated posts extending posteriorly from the scapular side of the glenoid component at generally the same oblique angle to the articulating surface as the insert's tab. The porous metal coating on the posts promote bone ingrowth therein for long term fixation of the glenoid component to the scapula. Since the posts and tab extend posteriorly from the scapular side of the glenoid component at an angle thereto, illustratively, at an oblique angle to the articulating surface, the glenoid component can be implanted anteriorly as opposed to laterally. This reduces the amount that the shoulder must be exposed and dislocated when the glenoid component is implanted.
The glenoid component can also include a plurality of opposed holes in its anterior facing surface for receiving posts of a glenoid positioner. The glenoid positioner has a handle with a T-head at a distal end thereof. The posts extend axially from opposed ends of the T-head. The glenoid component is held on the glenoid positioner by the posts of the glenoid positioner being received in the opposed holes in the anterior facing surface of the glenoid component. The glenoid positioner is used to manipulate the glenoid component and properly position it in the wound when it is being implanted.
The glenoid positioner is also used in conjunction with a control wire to properly position the humeral component before the humeral component is fully inserted into the canal in the humerus. The humeral component has a hole extending transversely through a proximal end from which the tapered post which receives the ball extends. A control wire is inserted into this hole and the glenoid positioner then reinserted into the glenoid component which has at this time been affixed to the scapula of the shoulder. The humeral component is then rotated so that the control wire is at approximately a desired angle to the handle of the glenoid positioner. The humeral component is then fully seated. The cooperation of the control wire with the handle of the glenoid positioner provides a better reference for determining when the humeral component is oriented properly with respect to the glenoid component.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment, exemplifying the best mode of carrying out the invention as presently perceived. The detailed description particularly refers to the accompanying figures in which: